Insulation Under Slab is becoming more common. By insulating below, the slab becomes part of the thermal mass of the property.

Insulated Under Slab

This type of floor is generally considered to be more energy efficient, whether you are heating the property with radiators or UFH.

A key point to note is that the insulation needs to be of sufficient density to take the weight above. The pipe is either secured to the slab using pipe clips or tied to a lightweight reinforcing mesh (D49 or similar) which is loose laid across the slab. Pipe spacing is generally 100mm from perimeters and 250mm centres.